p53 mutations have been detected in many tumors and interpreted as a late event in tumorigenesis, probably involved in tumor progression rather than tumor development. Recent studies have demonstrated the presence of germline p53 mutations in some Li-Fraumeni pedigrees and hence a role of p53 mutations in hereditary susceptibility to human cancer. Rhabdomyosarcoma, a common soft tissue sarcoma in the families with the Li-Fraumeni syndrome, was found to have p53 mutations. However, the frequency of such mutations in pediatric tumors remains unknown. We have recently established a non-radioisotopic method to detect mutations. This method is based on the formation of DNA hetero-duplexes with variable motility in mutation detection enhancement (MDE) gels. Mutations can thus be detected in PCR-amplified DNA extracted even from paraffin embedded tissues. Using this method, we have studied PCR fragments spanning exons 4, 5, 6, 7, and 8 of the p53 gene from 13 rhabdomyosarcomas (RMS) (mostly paraffin blocks). A high percentage of the studied tumors (46%) exhibited p53 mutations, more often in exon 7, followed by exons 8 and 5. The presence of mutations was confirmed in some cases with the standard single stranded conformational polymorphism (SSCP) method and with a direct sequencing method of single stranded DNA obtained by asymmetric PCR. We have currently expanded the study to include a larger number of RMS, as well as other solid pediatric tumors, such as neuroblastoma and peripheral and central PNET/Ewing's sarcoma cases. The survival of patients with mutated and non-mutated tumors will be compared to explore a potential prognostic role of p53 mutations in this group of tumors.